#include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>

using namespace std;

typedef long long lld;

const double eps=1e-7;

bool judge(int x,int y,int k)
{
  // printf("judge %d %d <= %d\n",x,y,k*k*4);
    return 1LL*x*x+3LL*y*y<=4LL*k*k;
}
lld getAns(int k)
{
    double sq3=sqrt(3);
    int x,y;
    lld ans=0;
    int cnt=0;
    for(y=1;true;y+=2)
    {
        if(judge(1,y,k)) cnt++;
        else
        {
            y-=2;
            break;
        }
    }
//cout<<cnt<<endl;
    cnt=cnt*2-1;
    ans+=cnt;
    x=1;
    while(true)
    {
        y+=1;
        x+=3;
        cnt++;
        while((!judge(x,y,k)||!judge(x+1,y-1,k))&&cnt>0) y-=2,cnt-=2;
        //cout<<cnt<<endl;
        if(cnt>0) ans+=cnt*2;
        else break;
    }
    return ans;
}
int main()
{
    int k;
    while(cin>>k)
        cout<<getAns(k)<<endl;
        return 0;
}
